Single photon avalanche diode (SPAD) time of flight sensors typically comprise arrays of single photon avalanche diodes and an illumination source in the form of a vertical cavity surface emitting laser (VCSEL). The vertical cavity surface emitting laser is provided with current by a driver circuit which is typically configured to be able to control the current through the laser in order to produce pulse or other waveform outputs.
Typically the vertical cavity surface emitting laser has a threshold current above which the laser is able to emit light (and similarly below which the laser does not emit anything).
However this threshold current level is not well defined and may change significantly based on many variables such as temperature and process variations.